241 research outputs found
Spatial Modulation Microscopy for Real-Time Imaging of Plasmonic Nanoparticles and Cells
Spatial modulation microscopy is a technique originally developed for
quantitative spectroscopy of individual nano-objects. Here, a parallel
implementation of the spatial modulation microscopy technique is demonstrated
based on a line detector capable of demodulation at kHz frequencies. The
capabilities of the imaging system are shown using an array of plasmonic
nanoantennas and dendritic cells incubated with gold nanoparticles.Comment: 3 pages, 4 figure
Oxide materials for emerging applications in photonics: introduction to the special issue
This is an introduction to the feature issue of Optical Materials Express on Oxide Materials for Emerging Applications in Photonics
Plasmon oscillations in ellipsoid nanoparticles: beyond dipole approximation
The plasmon oscillations of a metallic triaxial ellipsoid nanoparticle have
been studied within the framework of the quasistatic approximation. A general
method has been proposed for finding the analytical expressions describing the
potential and frequencies of the plasmon oscillations of an arbitrary
multipolarity order. The analytical expressions have been derived for an
electric potential and plasmon oscillation frequencies of the first 24 modes.
Other higher orders plasmon modes are investigated numerically.Comment: 33 pages, 12 figure
Angular redistribution of near-infrared emission from quantum dots in 3D photonic crystals
We study the angle-resolved spontaneous emission of near-infrared light
sources in 3D photonic crystals over a wavelength range from 1200 to 1550 nm.
To this end PbSe quantum dots are used as light sources inside titania inverse
opal photonic crystals. Strong deviations from the Lambertian emission profile
are observed. An attenuation of 60 % is observed in the angle dependent radiant
flux emitted from the samples due to photonic stop bands. At angles that
correspond to the edges of the stop band the emitted flux is increased by up to
34 %. This increase is explained by the redistribution of Bragg-diffracted
light over the available escape angles. The results are quantitatively
explained by an expanded escape-function model. This model is based on
diffusion theory and adapted to photonic crystals using band structure
calculations. Our results are the first angular redistributions and escape
functions measured at near-infrared, including telecom, wavelengths. In
addition, this is the first time for this model to be applied to describe
emission from samples that are optically thick for the excitation light and
relatively thin for the photoluminesence light.Comment: 24 pages, 8 figures (current format = single column, double spaced
OCIS codes: (240.6680) Surface plasmons, (050.1950) Diffraction gratings, (260.3800) Lumi-nescence
Abstract: We demonstrate a novel functionality of semiconductor nanowires as local sources for surface plasmon polaritons (SPPs). Photoexcited semiconductor nanowires decay non-radiatively exciting SPPs when they are on top of a metallic surface. We have investigated the anisotropic excitation of SPPs by nanowires by placing individual InP nanowires inside gold bullseye gratings. The gratings serve to couple SPPs to free space radiation that is detected with a scanning confocal microscope. The circular geometry of the grating allows to conclude that SPPs are preferentially generated in the direction along the nanowire axis
Directional control of weakly localized Raman from a random network of fractal nanowires
Disordered optical media are an emerging class of materials capable of
strongly scattering light. Their study is relevant to investigate transport
phenomena and for applications in imaging, sensing and energy storage. While
such materials can be used to generate coherent light, their directional
emission is typically hampered by their very multiple scattering nature. Here,
we tune the out-of-plane directionality of coherent Raman light scattered by a
fractal network of silicon nanowires. By visualizing Rayleigh scattering,
photoluminescence and weakly localized Raman light from the random network of
nanowires via real-space microscopy and Fourier imaging, we gain insight on the
light transport mechanisms responsible for the material's inelastic coherent
signal and for its directionality. The possibility of visualizing and
manipulating directional coherent light in such networks of nanowires opens
venues for fundamental studies of light propagation in disordered media as well
as for the development of next generation optical devices based on disordered
structures, inclusive of sensors, light sources and optical switches
Controlled reduction of photobleaching in DNA origami gold nanoparticle hybrids
The amount of information obtainable from a fluorescence-based measurement is limited by photobleaching: Irreversible photochemical reactions either render the molecules nonfluorescent or shift their absorption and/or emission spectra outside the working range. Photobleaching is evidenced as a decrease of fluorescence intensity with time, or in the case of single molecule measurements, as an abrupt, single-step interruption of the fluorescence emission that determines the end of the experiment. Reducing photobleaching is central for improving fluorescence (functional) imaging, single molecule tracking, and fluorescence-based biosensors and assays. In this single molecule study, we use DNA self-assembly to produce hybrid nanostructures containing individual fluorophores and gold nanoparticles at a controlled separation distance of 8.5 nm. By changing the nanoparticles? size we are able to systematically increase the mean number of photons emitted by the fluorophores before photobleaching.Fil: Pellegrotti, Jesica Vanesa. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂsica; ArgentinaFil: Acuña, Guillermo. Technische Universität Braunschweig. Institute for Physical and Theoretical Chemistry. NanoBioSciences Group; AlemaniaFil: Puchkova, Anastasiya. Technische Universität Braunschweig. Institute for Physical and Theoretical Chemistry. NanoBioSciences Group; AlemaniaFil: Holzmeister, Phil. Technische Universität Braunschweig. Institute for Physical and Theoretical Chemistry. NanoBioSciences Group; AlemaniaFil: Gietl, Andreas. Technische Universität Braunschweig. Institute for Physical and Theoretical Chemistry. NanoBioSciences Group; AlemaniaFil: Lalkens, Birka. Technische Universität Braunschweig. Institute for Physical and Theoretical Chemistry. NanoBioSciences Group; AlemaniaFil: Stefani, Fernando Daniel. Consejo Nacional de Investigaciones CientĂficas y TĂ©cnicas. Oficina de CoordinaciĂłn Administrativa Parque Centenario. Centro de Investigaciones en Bionanociencias "Elizabeth Jares Erijman"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de FĂsica; ArgentinaFil: Tinnefeld, Philip. Technische Universität Braunschweig. Institute for Physical and Theoretical Chemistry. NanoBioSciences Group; Alemani
Enhanced Lifetime Of Excitons In Nonepitaxial Au/cds Core/shell Nanocrystals
The ability of metal nanoparticles to capture light through plasmon excitations offers an opportunity for enhancing the optical absorption of plasmon-coupled semiconductor materials via energy transfer. This process, however, requires that the semiconductor component is electrically insulated to prevent a backward charge flow into metal and interfacial states, which causes a premature dissociation of excitons. Here we demonstrate that such an energy exchange can be achieved on the nanoscale by using nonepitaxial Au/CdS core/shell nanocomposites. These materials are fabricated via a multistep cation exchange reaction, which decouples metal and semiconductor phases leading to fewer interfacial defects. Ultrafast transient absorption measurements confirm that the lifetime of excitons in the CdS shell (tau approximate to 300 ps) is much longer than lifetimes of excitons in conventional, reduction-grown Au/CdS heteronanostructures. As a result, the energy of metal nanoparticles can be efficiently utilized by the semiconductor component without undergoing significant nonradiative energy losses, an important property for catalytic or photovoltaic applications. The reduced rate of exciton dissociation in the CdS domain of Au/CdS nanocomposites was attributed to the nonepitaxial nature of Au/CdS interfaces associated with low defect density and a high potential barrier of the interstitial phase
Active liquid crystal tuning of metallic nanoantenna enhanced light emission from colloidal quantum dots
A system comprising an aluminum nanoantenna array on top of a luminescent colloidal quantum dot waveguide and covered by a thermotropic liquid crystal (LC) is introduced. By heating the LC above its critical temperature, we demonstrate that the concomitant refractive index change modifies the hybrid plasmonic-photonic resonances in the system. This enables active control of the spectrum and directionality of the narrow-band (similar to 6 nm) enhancement of quantum dot photoluminescence by the metallic nanoantennas
A Novel Multi-Antigen Virally Vectored Vaccine against Mycobacterium avium Subspecies paratuberculosis
BACKGROUND: Mycobacterium avium subspecies paratuberculosis causes systemic infection and chronic intestinal inflammation in many species including primates. Humans are exposed through milk and from sources of environmental contamination. Hitherto, the only vaccines available against Mycobacterium avium subspecies paratuberculosis have been limited to veterinary use and comprised attenuated or killed organisms.
METHODS: We developed a vaccine comprising a fusion construct designated HAV, containing components of two secreted and two cell surface Mycobacterium avium subspecies paratuberculosis proteins. HAV was transformed into DNA, human Adenovirus 5 (Ad5) and Modified Vaccinia Ankara (MVA) delivery vectors. Full length expression of the predicted 95 kDa fusion protein was confirmed.
PRINCIPAL FINDINGS: Vaccination of naĂŻve and Mycobacterium avium subspecies paratuberculosis infected C57BL/6 mice using DNA-prime/MVA-boost or Ad5-prime/MVA-boost protocols was highly immunogenic resulting in significant IFN-gamma ELISPOT responses by splenocytes against recombinant vaccine antigens and a range of HAV specific peptides. This included strong recognition of a T-cell epitope GFAEINPIA located near the C-terminus of the fusion protein. Antibody responses to recombinant vaccine antigens and HAV specific peptides but not GFAEINPIA, also occurred. No immune recognition of vaccine antigens occurred in any sham vaccinated Mycobacterium avium subspecies paratuberculosis infected mice. Vaccination using either protocol significantly attenuated pre-existing Mycobacterium avium subspecies paratuberculosis infection measured by qPCR in spleen and liver and the Ad5-prime/MVA-boost protocol also conferred some protection against subsequent challenge. No adverse effects of vaccination occurred in any of the mice.
CONCLUSIONS/SIGNIFICANCE: A range of modern veterinary and clinical vaccines for the treatment and prevention of disease caused by Mycobacterium avium subspecies paratuberculosis are needed. The present vaccine proved to be highly immunogenic without adverse effect in mice and both attenuated pre-existing Mycobacterium avium subspecies paratuberculosis infection and conferred protection against subsequent challenge. Further studies of the present vaccine in naturally infected animals and humans are indicated
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